cprint ? adjustments

This is a result of testing 4.22 with cbl-gdb-4.2.2.vsix.

(gdb) cprint/r 999
(gdb) cprint ?
Variable not found

This should print something like "range printing disabled, explicit add the range". ... and that is the actual feature request:

Change cprint ? to cprint ? [range]. If range is not explicit specified it would be used whatever is configured (or the default of) cprint/r.

The main idea here is to later let the vsix extension don't use the range specified by cp/r but instead always ask with a configured range within the extension. This will also allow to have the automated variable context printing in the UI be disabled but still allow the feature to be used in the debugging console manually upon need (which was the reason for seeing "Variable not found" with cp ? during testing).

@sjaak Please feel free to reassign this issue to me if you don't want to handle it.